As network communication technology develops, usually there are special transmission demands for specific services in network communication. Therefore, it is necessary to control network resources to meet the transmission demands of specific services, e.g., restrict File Transfer Protocol (FTP) bandwidth on the backbone network, provide higher priority for database access, realize Internet Service Providers (ISP) providing different transmission for voice, video, and other real-time services and provide bandwidth and low time delay assurance for time-sensitive multimedia services.
To this end, Internet Protocol Quality of Service (IP QOS) technology appeared. IP QOS refers to the capability of providing services over IP networks, i.e., provide required service capability for specific flows across under-layer IP networks including Frame Relay (FR), Asynchronous Transfer Mode (ATM), Ethernet, and Synchronous Digital Hierarchy (SDH); usually, the technical criteria used to measure IP QOS include:
bandwidth/throughput: which refers to the mean velocity of flows for specific application between two nodes;
time delay: which refers to the average round-trip time of a data packet between two nodes in the network;
dithering: which refers to variation of the time delay;
loss rate: which refers to the percentage of lost packets during transmission in the network and is used to measure the capability of the network in forwarding subscriber data correctly;
availability: which refers to the percentage of the available service time during which the network can provide service for subscribers.
To implement the end-to-end QOS function in the communication network, usually each network element, e.g., router, Ethernet switch, etc., shall have the capability of classifying messages and providing different processing, queue management, and dispatching for different classes of messages to meet different QOS requirements of different services, as well as providing traffic supervision and control, traffic shaping, adjusting message output speed, and determining whether to allow the subscriber's data flow to use network resources.
IP QOS includes Resource Reserve Protocol-based (RSVP-based) Integrated Service (IntServ), which is an end-to-end flow-based QOS technology; with that technology, before communication, the applications at two ends shall set up an end-to-end communication path with out-of-band RSVP signaling according to class of service and the requirement for network resources, and each router along the path shall record state information of each flow and provide corresponding service assurance.
To seek for expansibility and simplicity, IETF organization has put forward Difference Service (DiffServ) technology, which is a class-based QOS technology and is mainly used in the backbone network; the technology classifies services, performs flow control, and sets DSCP (Difference Service Code Point) domain of the message at the network ingress according to requirements of services; it distinguishes communication types in the network according to the predefined QOS mechanism and provides policies, including resource allocation, queue dispatching, and packet discarding, for Per Hop Behave (PHB); all nodes in the DiffServ domain will obey PHB according to the DSCP field in packets.
To incorporate the advantages of above IntServ and DiffServ, Integrated Service over Difference Service (IntServ over DiffServ) model is developed, which presumes the two ends of the communication network support IntServ/RSVP and regards some domains that don't support IntServ/RSVP along the end-to-end path, e.g., DiffServ domain. The DiffServ domain is regarded as a virtual connection in the IntServ domain; flow-based RSVPs are transmitted transparently in the DiffServ domain to the other end; certain bandwidth is reserved between the two ends. As shown in FIG. 1, the bandwidth from the source end to ingress of the DiffServ domain and from egress of the DiffServ domain to the destination end is guaranteed; however, in the DiffServ domain, the bandwidth is only guaranteed for aggregate flows but may not be guaranteed for individual flows. To overcome the phenomenon, the DiffServ domain shall support Aggregate Resource Reserve Protocol (RSVP).
The aggregate RSVP collects flow-based RSVP requests at ingress node of the DiffServ domain, aggregates the requests, and then requests for a total bandwidth from the egress node of the DiffServ domain. When there is a new RSVP request or a Cancel request, the aggregate RSVP adjusts the reserved bandwidth between edges of the DiffServ domain. Since the total bandwidth is exactly the sum of the bandwidths of individual flows, end-to-end QOS assurance can be provided.
Even though IntServ over DiffServ technology can implement reasonable allocation of communication network resources, it has the following disadvantages:
(1) the technology is only applicable to IP network and is tightly coupled with RSVP; it applicability is limited;
(2) the technology is only suitable for aggregate model but is not suitable for peer-to-peer model;
(3) the resulting aggregate flow from data flows is solely determined by the network, and there is no interaction with the application terminals; therefore, the network has to maintain and manage a large quantity of resource allocation policy information;
(4) it has no aggregate bandwidth pre-allocation mechanism; instead, it employs first application flow-triggered establishment mechanism;
(5) there is no aggregate bandwidth allocation mechanism between the host and the Aggregator/De-Aggregator; therefore, in the Client/Server model, the Aggregator/De-Aggregator connected with the server has to support a large amount of data flow-based queues;
(6) it has no resource preemption mechanism.
As Multi-protocol Label Switch (MPLS) technology emerges, people begin to try to solve QOS problem of traffic transmission with MPLS, including MPLS DiffServ and MPLS TE. The combination of MPLS and DiffServ is referred to as MPLS DiffServ (or MPLS CoS), which means to aggregate DSCPs or labels at edge of the network and process DSCP-based PHB or label-based forwarding at core of the network. While MPLS TE utilizes LSP supporting route presentation capability and pilot network traffic on the premise of limited network resources so as to match the actual network traffic load with the physical network resources and thereby improving QOS of the network.
DS-Aware TE is a MPLS-based indirect QOS technology, which optimizes network resource utilization through reasonable resource configuration and effective control of routing process. Since MPLS incorporates Lay-2 and Lay-3 technologies, it has intrinsic advantages in solving traffic engineering. MPLS traffic engineering optimizes network performance through searching for possible paths that meet the requirements of traffic relay with a set of route-constraining parameters. During setup, MPLS LSP carries some constraint conditions, e.g., bandwidth, affiliation property, etc. and sets up a satisfactory path through calculating restricted routes.
However, as shown in FIG. 2, if the sum of all Expedite Forwarding-type (EF)-type LSP bandwidths exceeds 50% of the total bandwidth, the time delay will exceed M1 ms, which means the traffic transmission requirements can't be met. Therefore, the EF service bandwidth shall be controlled strictly within 50%. As shown in FIG. 3, suppose the bandwidth between A and E is 200M, the bandwidths between E and C, between C and D, between D and F, as well as between F and E are all 100M, and a 20M EF flow has been established on the path through A, E, F and D through calculation of restricted paths; if another 20M EF-type flow from A to D is to be established, but it is found through calculation at point A that the bandwidth on the path through A, E, F and D meets the requirement and is optimal; because it is unable to know whether the sum of LSP bandwidth for EF flow established at point E has exceeded 50% of the total bandwidth during the calculation of restricted routes, point A only knows there is an 80M bandwidth from point E to point F. Therefore, it is possible that the time delay for EF-type LSP established at point E is not guaranteed. A solution is to expand existing Multi-protocol Label Switch Traffic Engineering (MPLS TE), i.e., Multi-protocol Label Switch Difference Service-Aware Traffic Engineering (MPLS DS-Aware TE), to inform resource occupation information at point E of point A.
The basic idea of MPLS DS-Aware TE is to enhance the class-based constraint condition on the basis of original MPLS TE, i.e., the nodes in the MPLS DS-Aware TE domain disseminate resource and occupation information according to each subscriber-defined service class to each other through Interior Gateway Protocol (IGP); during the connection is set up, MPLS signaling protocol specifies not only bandwidth but also service type, EF or Assured Forwarding (AF), which specifies the type to which the resource pertains to, so that the network resources are utilized to the best according to the subscribers' demands.
However, the existing DS-Aware TE still has the following disadvantages: it is only applicable to MPLS network; it only solves the QOS problem in a single autonomous system (AS) but can't solve the QOS problem across ASs; in addition, it can not solve the end-to-end QOS problem and doesn't support multicast resource requests, and thus its applicability range is limited.